The present invention relates to an anti-fuse and a method for writing information into the anti-fuse, more specifically to an anti-fuse and a method for writing information into the anti-fuse which can realize low costs and micronization of semiconductor devices, etc.
A number of elements are integrated on a semiconductor chips, but all the elements do not always normally function. Methods for replacing defective elements by normal elements to improve yields are proposed.
To replace a defective element by a normal element, the circuit must be switched. Fuses are proposed as means for switching circuits.
The proposed semiconductor device will be explained with reference to FIGS. 14A and 14B. FIGS. 14A and 14B are sectional views of the proposed semiconductor device.
As shown in FIG. 14A, an insulation film 112 of SiO2 is formed on a semiconductor substrate 110 of silicon. An interconnection layer 114 of, e.g., Al is formed on the insulation film 112. An insulation film 116 is formed on the insulation film 112 with the interconnection layer 114 formed on. Openings 118 are formed in the insulation film 116 down to the interconnection layer 114. An interconnection layer 120 of Al is laid on the insulation film 116 with the openings 118 formed in with a barrier layer 119 of TiN or WN formed therebetween. The interconnection layer 120 is formed on both sides of the interconnection layer 114. Thus, a fuse 123 including the interconnection layers 114 is formed.
Inter-layer insulation films 124a to 124d and interconnection layers 126a to 126d are formed on the interconnection layer 120. An opening 140 is formed in the inter-layer insulation films 124a to 124d down to the interconnection layer 114.
Thus, the proposed semiconductor device is constituted.
The fuse 123 of such semiconductor device can be changed from the conduction state to the non-conduction state by the following way.
As shown in FIG. 14A, in the state that the interconnection layer 114 is not broken, the fuse 123 is in the conduction state.
As shown in FIG. 14B, an intense laser beam is applied to the interconnection layer 114 from above. When the intense laser beam is applied to the interconnection layer 114, a part of the interconnection layer 114 is melted and evaporated, and the interconnection layer 114 is broken. Thus, the fuse 123 is changed from the conduction state to the non-conduction state. A defective element is thus replaced by a normal element, and yields of the semiconductor device can be increased.
However, in the proposed semiconductor device shown in FIGS. 14A and 14B, in order to change the conduction state, a part of the interconnection layer 114 must be melted and scattered. Intense laser beams must be applied to the interconnection layer 114. In the proposed semiconductor device, unless an expensive equipment which can generate intense laser beams is used, the conduction state of the fuse cannot be changed.
In the proposed semiconductor device, in which the above-describe intense laser beams must be applied, neighboring fuses 123 must be considerably spaced from one another in order to prevent other neighboring fuses 123 which are not to be changed to the non-conduction state from being changed to the non-conduction state. Accordingly, in the proposed semiconductor device, fuses cannot arranged in high density, which makes a region for a plurality of fuses 123 to be arranged considerably large.
In the proposed semiconductor device, in order to change the fuse 123 from the conduction state to the non-conduction state by melting and evaporating a part of the interconnection layer 114, the opening 140 must be formed down to the interconnection layer 114 so that the melted metal can be evaporated. Accordingly, the step of forming the opening 140 is necessary.
In the proposed semiconductor device, it is not easy to form in the inter-layer insulation films 124a to 124d the opening 140 deep down to the lower layer. Accordingly, the proposed semiconductor device has low freedom of design.
In the proposed semiconductor device, in many cases, the fuse 123 is formed near the upper layer, which often makes a width of the interconnection layer 114 large. This is because usually micronization processing is not used near the upper layer. In the proposed semiconductor device, without melting and evaporating the wide interconnection layer 114, the fuse 123 cannot be changed from the conduction state to the non-conduction state. Accordingly, in the proposed semiconductor device, an intensity of laser beams to be applied must be set high, and a time of applying laser beams must be set considerably long.
The use of anti-fuses makes redundancy circuits simple than the use of the fuses 123. The development of the anti-fuse is awaited.